Aggregation in Nanobundles and the Effect of Diverse Environments on the Solution-Phase Photochemistry and Photophysics of− Re (CO) 3L (L) 1, 10- … (original) (raw)
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Inorganic Chemistry, 2006
The UV−vis spectroscopy and photochemical properties of {(vpy-[Re(CO) 3 (2,2′-bpy)]) m (vpy-[Re(CO) 3 (phen)]) n (vpy) p }-(CF 3 SO 3 ) m+n }, vpy ) 4-vinylpyridine, m ) 131, n ) 131 or m ) 200, n ) 150, and m + n + p ) 600, were investigated in solution phase. The polymers exist in solution as aggregates of polymer strands with radii as large as ∼10 2 nm. Given the size of the poly-vpy backbone, the aggregates must contain a large number of strands. The luminescence spectrum exhibits a strong resemblance to the emission spectrum of {(vpy-[Re(CO) 3 (phen)]) 200 -(vpy) 400 }(CF 3 SO 3 ) 200 . The existence of Re(I) chromophores in diverse environments was shown by the intrinsic kinetics of the luminescence, the decay kinetics of the MLCT excited states observed by time resolved-absorption spectroscopy, and the quenching of the luminescence by various quenchers. Redox reactions of the MLCT excited states with the quenchers were responsible for the luminescence quenching. While static quenching resulted when Cu(II) and Fe(III) EDTA complexes were the quenchers, a dynamic quenching resulted with Fe(CN) 6 4or 2,2′,2′′triethanolamine, TEOA. The photochemical and photophysical properties of the mixed-pendant polymers have been discussed in terms of arrays of MLCT excited states whose energies are determined by the diverse environments of the Re(I) chromophores. Conversions (with and without radiation) of the upper-energy MLCT excited states to the ground state and lower-energy MLCT excited states and the latter excited state to the ground state account for the experimental results.
Photochemical & Photobiological Sciences, 2003
Solvent and temperature effects on the photophysical properties of the polymer {[(vpy) 2 -vpyRe(CO) 3 2,2Ј-bipyridine] CF 3 SO 3 } n∼200 and the related monomer CF 3 SO 3 [pyRe(CO) 3 2,2Ј-bipyridine] were investigated in solution by flash photolysis at 337, 351 and 355 nm and by steady state irradiations. MLCT excited states in the polymer undergo a more efficient annihilation than in the monomer. Differences between the polymer and the monomer photophysical behavior are rationalized in terms of solvent and thermal effects on the transition between rigid rod and coil structures of the Re(I)-polymer.
Photochem. Photobiol. Sci., 2003
Solvent and temperature effects on the photophysical properties of the polymer {[(vpy) 2 -vpyRe(CO) 3 2,2Ј-bipyridine] CF 3 SO 3 } n∼200 and the related monomer CF 3 SO 3 [pyRe(CO) 3 2,2Ј-bipyridine] were investigated in solution by flash photolysis at 337, 351 and 355 nm and by steady state irradiations. MLCT excited states in the polymer undergo a more efficient annihilation than in the monomer. Differences between the polymer and the monomer photophysical behavior are rationalized in terms of solvent and thermal effects on the transition between rigid rod and coil structures of the Re(I)-polymer.
J Phys Chem a, 2000
The photochemical and photophysical properties of a polymer containing nearly 200 pendant groups Re-(CO) 3 (1,10-phenanthroline) + bonded to poly-(vynilpyridine) 600 and the related monomer pyRe(CO) 3 (1,10phenanthroline) + were investigated in solution phase. The yield of formation and the kinetics of decay of the MLCT excited state were found to be dependent on medium and laser power. MLCT excited states in the polymer undergo a more efficient annihilation and/or secondary photolysis than in the monomer. In the polymer, redox quenching of MLCT excited states by methyl viologen and by 2,2′,2′′-nitrilotriethanol revealed the presence of intrastrand electron-transfer processes. These processes exhibited a complex kinetics. Mechanisms of the excited-state annihilation and electron-transfer processes in the polymer are proposed.
Science Reviews - from the end of the world
We review the morphological and the photophysical properties of several inorganic polymers that can be prepared from poly-4- vinylpyridine (P4VP). These polymers contain –Re(CO)3(N^N)+ pendants attached to their backbone with α-diimine ligands (N^N) such as 2,2´-bipyridine (bpy), 1,10-phenanthroline (phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) and 5-nitro-1,10- phenanthroline (NO2-phen). These Re(I) polymers, show marked differences in their photophysical properties when compared to single [pyRe(CO)3(N^N)]+ molecules in diluted solutions. For example, Re→phen charge transfer excited states (MLCT) in the Re(I) polymers undergo a more efficient annihilation and/or secondary photolysis than in [pyRe(CO)3phen]+ complexes. Depending on solvent and/or cast film conditions, several aggregates of polymer strands with different morphologies were observed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. Morphological changes derived from med...
Journal of Photochemistry and Photobiology A: Chemistry, 2016
Photochemical and photophysical properties of a polymer, Re-P4VP, consisting of À ÀRe(I)(CO) 3 (phen) pendants grafted to a poly-4-vinylpyridine backbone, P4VP, were interpreted on the bases of morphological transformations. These transformations are responsible of a significant increase of the MLCT Re(I)!phen excited state luminescence lifetime when the polymer concentration is increased. Also a nearly 8-fold increase in the luminescence quantum yield resulted from the protonation of Re-P4VP with consequent changes of the excited state decay kinetics. Results of TEM and AFM morphological studies on P4VP and Re-P4VP in the presence of HClO 4 acid, i.e., to form Re-P4VPH n n+ , revealed that they have concentration dependent morphologies. From low to large concentrations of the Re-P4VP polymer, the morphology of Re-P4VP varies from a nonhomogeneous distribution of spherical nanoaggregates coexisting with micrometer size fibers to an homogeneous distribution of spherical nanoaggregates with diameters around 25 nm. The Re-P4VP morphology is also altered when the polymer pyridines are protonated. Protonation of diluted solutions of Re-P4VP polymers decrease the sizes of the nanoaggregates and small objects with diameters smaller than 10 nm appear.
On the Quenching of MLCT Re → b py Luminescence by Cu(II) Species in Re(I) Polymer Micelles
The Journal of Physical Chemistry B, 2005
Transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies on acetonitrile solutions of the polymer {[(vpy) 2 -vpyRe(CO) 3 bpy] CF 3 SO 3 } 200 demonstrated that the Re(I) polymer molecules aggregate to form spherical micelles of radius R ) 156 nm. Coordination of Cu(II) species to the Re (I) polymer causes a decrease in the micelle radius and a distortion from the spherical shape. Besides, the coordination of Cu(II) species to the {[(vpy) 2 -vpyRe(CO) 3 bpy] CF 3 SO 3 } 200 polymer produces the quenching of the metal to ligand charge transfer (MLCT) excited state by energy transfer processes that are more efficient than those in the quenching of the monomer pyRe(CO) 3 bpy + luminescence by Cu(II). Moreover, the kinetics of the quenching by Cu(II) do not follow a Stern-Volmer behavior. Conversely, the quenching of the MLCT luminescence of the Re(I) polymer by the sacrificial electron donor 2,2′,2′′-nitrilotriethanol, TEOA, follows a Stern-Volmer kinetics. A comparison is made between the quenching by CuX 2 (X ) Cl or CF 3 SO 3 ) and TEOA.
Inorganic Chemistry, 2002
Steady-state and time-resolved spectroscopic properties of bichromophoric species containing [Ru(bpy) 3 ] 2+ and pyrene (pyr) units linked together by flexible poly(ethylene glycol) chains of variable length, [Ru(bpy) 2 (bpy-pyr)]-(PF 6 ) 2 (1) and [Ru(bpy) 2 (bpy-O6-pyr)](PF 6 ) 2 (2), have been investigated in acetonitrile solvent. The complexes were designed with the aim of examining the intercomponent energy-transfer processes taking place after light absorption at the two chromophores and the influence of the distance separation between them; in the case of complex 2, the linking chain in the extended conformation is as long as 21 Å. Direct excitation of the pyrene unit (λ exc ) 410 nm) results in singlet-to-singlet energy transfer (an antenna effect) to the Ru-based component, 1 pyr f 1 MLCT, which we analyze in terms of the Förster mechanism taking place with unit efficiency. Analysis of the time-resolved pyrene fluorescence reveals that the actual center-to-center distance separation (d cc ) between the photoactive centers changes according to a Gaussian distribution, with an average d cc ) 13.6 Å (distribution width, a ) 2.8 Å) and 12 Å (a ) 10.2 Å), for 1 and 2, respectively; this is ascribed to folding of the poly(ethylene glycol) linking chain. In O 2 -free solvent at room temperature, after population of the 1 MLCT level (which takes place either because of direct excitation by using λ exc > 355 nm or via the "antenna" effect) and subsequent intersystem crossing localized at the Ru center, 1 MLCT f 3 MLCT, a triplet−triplet thermal equilibration is established which involves the physically separated centers, 3 MLCT T 3 pyr, with K eq ) 11 (the energy gap between the two levels is 480 cm -1 , as determined from luminescence data obtained at 77 K). As a consequence of this equilibrium, the 3 MLCT luminescence lifetime becomes τ Ru ∼ 9 µs both in 1 and 2, i.e., 1 order of magnitude longer than for the unsubstituted [Ru(bpy) 3 ] 2+ luminophore. In air-equilibrated solvent, diffusional quenching by O 2 effectively depletes the 3 pyr level and only the forward 3 MLCT f 3 pyr energy transfer step is observed with k en ) 4 × 10 8 and 2 × 10 8 s -1 for 1 and 2, respectively. As briefly discussed, reasons for the high rate constants observed for the various triplet−triplet steps may be traced back to the folding properties of the linking chains. (F.B.). † Dedicated to Prof. Vincenzo Balzani, in recognition of his contribution to the development of inorganic photochemistry. ‡ Istituto ISOF-CNR, Bologna. § University of Bristol. (1) Wasielewski, M. R. Chem. ReV. 1992, 92, 435.
The Journal of Physical Chemistry B, 2008
Polymers with general formula {[(vpy) 2 vpyRe(CO) 3 (tmphen) + ]} n {[(vpy) 2 vpyRe(CO) 3 (NO 2 -phen) + ]} m (NO 2phen ) 5-nitro-1,10-phenanthroline; tmphen ) 3,4,7,8-tetramethyl-1,10-phenanthroline); vpy ) 4-vinylpyridine) were prepared and their morphologies were studied by transmission electron microscopy (TEM). Multiple morphologies of aggregates from these Re I polymers were obtained by using different solvents. Energy transfer between MLCT Reftmphen and MLCT RefNO 2 -phen excited states inside the polymers was evidenced by steady state and time-resolved spectroscopy. Current Förster resonance energy transfer theory was successfully applied to energy transfer processes in these polymers.
Photophysics and Redox Behavior of Chiral Transition Metal Polymers
Inorganic Chemistry, 2003
The absorption and emission spectra, excited-state lifetimes, quantum yields, and electrochemical measurements have been obtained for a new series of chiral complexes based on three different chiral 2,2′:6′,2′′-terpyridine ligands, (−)-ctpy, (−)-[ctpy-x-ctpy], and (−)-[ctpy-b-ctpy], with one, two, or multiple Ru metal centers. The roomtemperature absorption and emission maxima of {[((−)-ctpy)Ru]-(−)-[ctpy-b-ctpy]-[Ru((−)-ctpy)]}(PF 6) 4 and ((−)-[ctpy-b-ctpy])-{[Ru((−)-[ctpy-b-ctpy])](PF 6) 2 } n were shifted to lower energies and also exhibited significantly longer luminescence lifetimes when compared to [Ru((−)-ctpy) 2 ](PF 6) 2 , {[((−)-ctpy)Ru]-(−)-[ctpy-x-ctpy]-[Ru((−)-ctpy)]}-(PF 6) 4 , and ((−)-[ctpy-x-ctpy])-{[Ru((−)-[ctpy-x-ctpy])](PF 6) 2 } n. In terms of their electrochemical behavior, all of the complexes studied exhibited one Ru-centered and two ligand-centered redox waves and the {[((−)-ctpy)Ru]-(−)-[ctpy-x-ctpy]-[Ru((−)-ctpy)]}(PF 6) 4 , ((−)-[ctpy-x-ctpy])-{[Ru((−)-[ctpy-x-ctpy])](PF 6) 2 } n , and ((−)-[ctpy-b-ctpy])-{[Ru-((−)-[ctpy-b-ctpy])](PF 6) 2 } n complexes were found to electrodeposit upon ligand-based reduction. The difference between the formal potentials of the Ru-centered and the first ligand-centered (least negative) waves corresponded linearly with the changes in the observed emission energies. The shifts in energy are discussed using a particlein-a-box model, and the luminescence lifetimes are discussed in terms of the structure of the excited-state manifold.